Questions continue to swirl in the wake of Michael Flynn's resignation as national security adviser, including which White House officials knew -- and when -- about Flynn's calls with the Russian ambassador to the U.S. during the Trump administration transition.

According to White House press secretary Sean Spicer, President Trump was informed of the Justice Department's findings in a briefing from his White House counsel on Jan. 26.

Flynn wrote in his resignation letter that he "inadvertently briefed the Vice President-elect and others with incomplete information regarding my phone calls with the Russian Ambassador," but questions about the legality of the calls remain at large.

Crucial questions

Administration sources confirmed to ABC News that the Justice Department, under the direction of then-acting Attorney General Sally Yates, had informed the Trump administration after Jan. 20 that Flynn may have misled Vice President Mike Pence and other senior White House officials about his calls with the Russian ambassador, Sergey Kislyak.

Flynn had previously confirmed that he had spoken to the ambassador, but denied that the sanctions imposed on Russia by the U.S. for its suspected interference in the 2016 election were mentioned -- a discussion that may have violated federal law. Pence had publicly defended Flynn, saying that he had called Kislyak to wish him a Merry Christmas and to offer condolences after a deadly Russian plane crash. Administration officials noted that the vice president was relying on information provided to him by Flynn.

Flynn later said that he "can't be certain" if sanctions were brought up in the conversations.

It wasn't until Friday, Feb. 10, that Flynn apologized to Pence and other officials for misleading them about the details of his discussion with the Russian ambassador, sources told ABC News.

After Trump was reportedly told about the situation on Jan. 26, there was a roughly three week period between the time the Justice Department notified the White House and when Flynn apologized to Pence and other officials. During that time, no efforts were made to correct or clarify Pence's statements about Flynn's conversations with the ambassador.

Spicer explained to reporters Tuesday that the delay was due in part because the president had asked the White House counsel to review the situation and see if there was a legal issue with Flynn's actions. Spicer said the White House counsel determined there was not.

Last Friday, however, when Trump was asked on Air Force One whether he had heard of reports that Flynn had spoken with the Russian ambassador about sanctions, he replied, "I don't know about it. I haven't seen it. What report is that?"

Spicer said today that Trump was referring specifically to the Washington Post's initial report on the story.

"The evolving and eroding level of trust as a result of this situation and a series of other questionable instances is what led the president to ask for General Flynn's resignation," Spicer said.

Spicer did not clarify what other "questionable instances" contributed to the president's decision.

Sen. John McCain, R-Ariz., told ABC News Tuesday that there are "lots of questions about it, yeah there's lots of questions."

"Obviously there's an administration that is in significant disarray as far as national security is concerned and they need to fix that," he said.